title: Effects of iontophoresed opioids on physiologically characterized laminae I and II dorsal horn neurons in the cat spinal cord.
abstract: The objective of the present study was to determine in vivo the effects of opioids applied locally via microiontophoresis on physiologically characterized laminae I and II dorsal horn neurons in the cat spinal cord. Experiments were performed on pentobarbital-anesthetized or decerebrate, spinalized cats. The effects of morphine (MOR), [D-Ala2,methyl-Phe4, Gly-ol5]enkephalin (DAGO) and naloxone (NALO) on spontaneous- and D,L-homocysteic acid-evoked unit activity were examined for 94 laminae I and II dorsal horn neurons. MOR, DAGO and NALO produced mixed effects (i.e., excitation or inhibition) on unit activity; however, the majority of cells examined (67%) were inhibited. Whether MOR, DAGO or NALO exerted excitatory or inhibitory influences on unit activity did not depend on the modality of the neuron (66% of high threshold units, 56% of multireceptive units and 69% of low threshold units were inhibited; some cells of each modality also were excited). NALO also was found rarely to be neutral; 75% of the cells examined were inhibited and 16% excited by NALO. Since NALO was found to itself have significant effects on laminae I and II dorsal horn unit activity, the ability to use NALO as an opioid antagonist to MOR and DAGO was confounded.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Oklahoma, Oklahoma City 73190.
authors.forename: S L
authors.initials: SL
authors.lastname: Jones
authors.forename: M J
authors.initials: MJ
authors.lastname: Sedivec
authors.forename: A R
authors.initials: AR
authors.lastname: Light
mesh_terms: D000818:Animals; D002415:Cats; D003655:Decerebrate State; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004745:Enkephalins / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007478:Iontophoresis; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects*; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects*
chemical_list: D004745:Enkephalins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D009020:Morphine